The appearance of corotating Keplerian discs orbiting Kerr superspinars
has been shown to be strongly dependent on the value of the superspinar
spin in both their shape and frequency shift profile, demonstrating
clear distinctions from the corotating discs around black holes.
However, it has to be modified in the innermost parts of the disc by the
self-illumination effect caused by the photons trapped in the strong
gravitational field near the superspinars with spin a < 9. Here we
demonstrate that self-illumination is irrelevant for counter-rotating
Keplerian discs orbiting in the field of all Kerr superspinars since
such discs are located at the regions where none of the radiated photons
can be trapped. Therefore, the results obtained by considering the
escaping photons only are quite relevant for the appearance of the
counter-rotating Keplerian discs orbiting Kerr superspinars. The
appearance and spectral continuum of such discs differ from those of
counter-rotating discs in the field of Kerr black holes. The differences
are of quantitative character except the existence of the disc images
located inside the image of the inner edge of the disc that are created
by photons reaching regions close to the surface of Kerr superspinars.
Their observational relevance is realistic in the near future for
accretion phenomena in the vicinity of Sgr A*.
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Relevant properties of test-particle equatorial circular orbits in the Kerr-anti-de Sitter spacetimes, including their existence, stability and orientation, are briefly discussed.
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Marginally stable perfect fluid tori with uniform distribution of specific angular momentum are determined in the Reissner-Nordström-(anti-)de Sitter black-hole and nakedsingularity spacetimes. Toroidal configurations are allowed only in the spacetimes admitting existence of stable circular geodesics. The configurations with equipotential surfaces crossing itself in a cusp allow accretion (inner cusp) and/or excretion (outer cusp) of matter from the toroidal configuration.
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We study properties of the off-equatorial motion of charged particles near compact objects endowed with magnetic fields. We pay attention to the circular orbits as well as to the general motion in the related off-equatorial potential `halo lobes'.
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Pseudo-Newtonian gravitational potential for spherically symmetric black-hole space-times with a repulsive cosmological constant is applied to equilibrium toroidal configurations of barotropic perfect fluid orbiting black holes. The results are presented for marginally stable barotropic tori with uniform distribution of the specific angular momentum. For the adiabatic (isoentropic) perfect fluid, temperature profiles, mass-density and pressure profiles are calculated.
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The influence of the observed relict vacuum energy on the fluctuations of CMBR going through cosmological matter condensations is studied in the framework of the Einstein-Strauss-de Sitter vakuola model. It is shown that refraction of light at the matching surface of the vakuola and the expanding Friedman universe can be very important during accelerated expansion of the universe, when the velocity of the matching surface relative to static Schwarzchildian observers becomes relativistic. Relevance of the refraction effect for the temperature fluctuations of CMBR is given in terms of the redshift and the angular extension of the fluctuating region.
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Rotating black holes in the brany universe of the Randall—Sundrum type with infinite additional dimension are described by the Kerr geometry with a tidal charge b representing the interaction of the brany black hole and the bulk spacetime. For b < 0 rotating black holes with dimensionless spin a > 1 are allowed. We investigate the role of the tidal charge in the orbital resonance model of quasiperiodic oscillations (QPOs) in black hole systems.
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We present equation of state of dense nuclear matter based on relativistic Brueckner—Hartree—Fock theory. The models of static neutron stars are calculated. The results are compared with neutron star models based on Skyrme equations of state and with models of strange stars following MIT bag model.
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We present estimates on the efficiency of neutrino trapping in brany extremely compact stars, using the simplest model with uniform distribution of energy density, assuming massless neutrinos and uniform distribution of neutrino emissivity. Computation have been done for two different uniform-density stellar solution in the Randall-Sundrum II type braneworld, namely with the Reissner-Nordström-type of geometry and the second one, derived by Germani and Maartens.1 Read More
We investigate the role of the tidal charge in orbital models of high-frequency quasiperiodic oscillations (QPOs) observed in neutron star binary systems. We show how the standard relativistic precession (RP) model modified by the tidal charge fits the observational data, giving estimates of the allowed values of the tidal charge and the brane tension based on the processes going in the vicinity of neutron stars. We compare our strong field regime restrictions with those given in the weak field limit of solar system experiments.
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